N-linked glycosylation of proteins is a fundamental and important post-translational modification found both in eukaryotes and in prokaryotes. This protein modification results in the covalent attachment of an oligosaccharide onto asparagine residues of polypeptide chains. Glycans are typically the most important interface between cells and their environment. As a vital constituent of all living systems, glycans are involved in most of the essential biological processes such as protein folding, cell signaling, fertilization, embryogenesis, and the proliferation of cells and their organization into specific tissues. Abnormal cell surface glycosylation and/or glycan-profiles are usually related to diseases such as cancer and atherosclerosis. Accordingly, altered glycosylation is an indication of an early and possibly critical point in development of human pathologies. Thus, insights into the carbohydrate related biological and pathological processes, and for developing diagnostics and therapeutics for human diseases.
The biosynthesis of complex oligosaccharides generally results in tremendous complexity and diversity, mainly due to the variable and multiple connectivity of glycan building blocks (monosaccharides). These cell-identifying glycosylated molecules include glycoproteins and glycolipids and are specifically recognized by various glycan binding molecules such as lectins, antiglycan antibodies, chemical compounds and also other glycans and glycolipids, etc. However, the enormous complexity of these interactions, and the lack of well-defined glycan libraries and analytical methods have been shown to be major obstacles in the development of glycomics. Moreover, naturally occurring glycans are typically isolated in tiny amounts and exist only as admixtures of isomers. As such, the limited availability and limited purity of said naturally occurring glycans do not allow their use as a reliable source of well-characterized oligosaccharides. Thus, novel synthesis methods are useful for the preparation of diverse glycan libraries for biological and structural applications.
The development of nucleotide and protein microarrays has revolutionized genomic, gene expression and proteomic research. Similarly, the development of glycan microarrays has allowed an unprecedented high-throughput exploration of the specificities of a diverse range of glycan-binding molecules. The systematic arrangement of glycans on arrays allow for efficient probing of low affinity protein-glycan interactions through multivalent presentation. Since their establishment, various types of “arrays” have been developed, including the one available from the Consortium of Functional Glycomics (CFG) which contains more than 600 oligosaccharides on an N-hydroxysuccinimide (NHS)-activated glass slide. However, the spacer group and immobilization chemistry used in different array formats clearly result in differences in the density, distribution and orientation of glycan presentation, which dramatically affects the binding affinity and even specificity in glycan-protein interactions. Therefore, cross-comparison among different array platforms and development of new glycan arrays to improve the sensitivity of detection, for example, of hetero-ligand bindings are particularly important. Moreover, pharmaceutical companies and research institutions would greatly benefit from glycan arrays for various screening and drug discovery applications, including arrays that facilitate analysis of the structural elements of glycans that contribute to binding to glycan binding molecules including antibodies, receptors and other biomolecules.